1. Field of the Invention
The invention relates to a dual-clutch transmission for motor vehicles, having two transmission subsections, a dry dual clutch, which transmits the torque from the engine to one or the other of the two transmission subsections, and a cooling system having a fan impeller for cooling the dual clutch.
2. Description of the Prior Art
Dual clutch transmissions are automatic shift transmissions, which allow a fully automatic gear change without an interruption in power by means of two transmission subsections. The transmission controller chooses the gears automatically or according to driver requirements within the permitted engine speed ranges. Torque is transmitted via one of the two clutches, which connect the two transmission subsections to the engine. While one clutch is closing, the other opens.
Dry dual clutches of this kind often may have inadequate cooling and are susceptible to overheating particularly in the case of small engines, where there is a need for frequent gear changes and the clutch disks are subject to high slip loading, especially when starting off or in stop-and-go mode. In parallel with the overheating, troublesome clutch odor can occur in the passenger compartment when using specific friction linings.
A dual clutch transmission with active air cooling is already known from DE 10 2010 007 198 A1. To generate the cooling air stream, use is made of a fan impeller, which is seated on one of the output shafts of the dual clutch or on one of the transmission input shafts. In this known version, only the starting clutch is cooled. With a cooling system of this kind, the required cooling capacity cannot be provided at high slip speeds.